Apparatus for bending a laminated plastic sheet

ABSTRACT

An apparatus for bending a laminated thermoplastic sheet without displacing the lamina relative to one another includes a clamp which functions to hold the sheet during the bending procedure. A support is disposed adjacent the clamp and has a curved surface for forming a bend in the sheet and a flat surface which constitutes an abutment for the part of the sheet being bent. The support is adjustable to vary the angle of bending. A bending device for the sheet comprises a carriage having a bending roller, and a ram whose size approximates that of the flat abutment surface. The sheet is clamped with a portion thereof projecting freely above the flat abutment surface and heated. The bending roller thereupon forces the sheet against the curved surface to bend the sheet and then moves across the projecting portion of the sheet to urge such portion into engagement with the flat abutment surface. Once the roller has completed its travel across the projecting portion of the sheet, the ram is applied to the projecting portion and holds it against the flat abutment surface until the sheet is cooled. The carriage is guided in a track having two sections of which one is parallel to and adjustable with the support.

BACKGROUND OF THE INVENTION

The invention relates to a method of thermoforming a laminated plasticsheet and to a device for bending thermoplastic laminated plasticsheets.

A method of shaping a laminated plastic sheet is known from the Austrianpatent 349 766. In this known method, the region of the sheet to be bentis heated and the sheet is thereupon bent, around a mandrel ifnecessary, in a bending device. Here, the individual lamellae of thesheet shift relative to one another. Elements serving for shaperetention then hold the bent component until the thermoplastic hashardened.

This known method employs a bending toggle which carries a bending plateand is pivoted about a bending mandrel. The bending plate is in constantsurface-to-surface contact with the marginal sheet portion to be bentand slides relative to the surface thereof. This sliding motion over alarge area is undesired. Since the bending plate lies against the sheetto be bent via an antifriction liner to avoid damage to the surface ofthe sheet, this bending device cannot hold the bent sheet until thesheet has hardened. Accordingly, a shape retention device isadditionally required. The shape retention device includes a pressingdie having a concave cylindrical pressing surface which, after thebending procedure, is pressed against the convex surface of the bentsheet portion. This pressing die must be different for each bendingradius. Therefore, even the holder of the Austrian patent 349 766considers the method and device of the patent to be capable ofimprovement.

A method of this type is known from WO 86/02314. In this known method,the bending device is again in surface-to-surface contact with themarginal sheet portion to be bent throughout at least a large part ofthe bending procedure. As a result, an undesired shifting of the layersrelative to one another occurs at the actual bending location of thesheet to be bent because the bending load is applied far from thisactual bending location.

In the device known from the generic WO 86/02314, the pressing member ismounted strictly for up-and-down movement so that only bends of 90degrees can be obtained, i.e., the method can only be applied to sheetswhose margins are to be bent 90 degrees.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the invention to improve the known method in such amanner that the actual bending load is uniformly applied to the marginalsheet portion to be bent during the entire bending procedure. A pulltowards the free sheet margin is to be exerted on the laminate layerswhile this bending load is applied so that the sheet is rigidly stressedat the actual bending location.

Another object of the invention is to improve the generic device suchthat a sheet can be bent in any manner. A single operating device is tocontain the arrangement which initiates and performs the bendingprocedure and such arrangement is to simultaneously exert a pull on thesheet layers to be bent and, following the bending procedure, apply anareal load to the bent section.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 to 4 show a bending device during bending,

FIG. 5 shows a different position of the bending device,

FIGS. 6 and 7 show the region of the bending location of the deviceaccording to the invention on a greatly enlarged scale to clarify thedesign of such region.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the drawings 1 denotes a laminated plastic sheet to be bent. Thesheet 1 is of a type known per se and is made up of severalthermoplastic laminate layers. Layers composed of thermoplastic bindersare interposed between these laminate layers.

The sheet 1 rests in a clamping device 7 which defines an upper clampingsurface 8 and a lower clamping surface 9. The free marginal sheetportion 2 of the sheet 1, which is to be bent, projects beyond the upperand lower clamping surfaces in the direction of the arrow F4. In theillustrated exemplary embodiment, the sheet 1 is to be bentapproximately 45 degrees in the region of a curved reaction surface 4.The lower clamping surface 9 continues as a so-called load reactionsurface 10 which is pivotally connected to the lower clamping surface 9at 23 so that the load reaction surface 10 can be set at the desiredbending angle.

The upper clamping surface 8 can be firmly applied against the sheet 1,and thus against the lower clamping surface 9, by hydraulic, pneumaticand/or mechanical means not illustrated in the drawing to thereby fixthe sheet 1 to be processed.

A bending device 3 is further provided and consists essentially of apressing ram 5 having a lower loading surface 11, and a loading roller 6which is of one piece with the pressing ram 5 and is vertically adjacentto the sheet 1. The pressing ram 5 is located vertically above andadjoins the loading roller 6. The pressing ram 5 and the loading roller6, which can be arrestable if necessary, can be moved towards theclamping device 7 by a hydraulic or pneumatic piston-and-cylinder unit18 which can, for example, be supported on the housing of the bendingdevice 3. Preferably, the pressing ram 5 and the loading roller 6 arethen guided via a guide 24 in the interior of the housing of the bendingdevice 3. Adjustment takes place at an inclination to the surface sothat, under final load, a pull is exerted on the plastic sheet.

The bending device 3 itself is guided in a carriage guide 12 which isdivided into two parts, namely, an upper part 15 and a lower part 14. Asshown particularly clearly in FIG. 1, the two parts can make an anglewith one another in that the lower part 14 of the carriage guide 12carries the load reaction surface 10 which is pivotally connected to theclamping surface 9 at 23.

The lower part 14 of the carriage guide 12 has a reaction abutment 20which surrounds the lower carriage guide and is provided with a loadreaction plate 25. A loading piston 26 of a hydraulicpiston-and-cylinder unit 19, which is located in the interior of thebending device 3 and is likewise connected to the pressing ram 5, can beapplied against the load reaction plate 25.

The bending device 3 has rollers 16 which support and guide it in thecarriage guide 12. The entire bending device 3 is equipped with aconnecting part 17 which leads to a loading unit for moving the bendingdevice 3 up-and-down.

The effect and operation of this arrangement are as follows:

In FIG. 1, the arrangement is in its starting position, i.e., the sheet1 rests on the lower clamping surface 9, the upper clamping surface 8has not yet been moved down to fix the sheet 1 and the bending device 3is in a starting rest position.

FIG. 2 shows that the upper clamping surface 8 has been moved downwardsin the direction of the arrow F1 of FIG. 1 thereby fixing the sheet 1and that the pressing ram 5 and the loading roller 6 were subsequentlymoved forwards in the direction of the arrow F2 by activating thehydraulic piston-and-cylinder unit 18. The loading roller 6 is nowsituated very near the bending location, i.e., the curved reactionsurface 4. The loading roller 6 generates a loading line which, forinstance, is transverse to the longitudinal direction F4 and thegeneratrix of the curved reaction surface 4.

According to FIG. 3, a load has been exerted on the bending device 3 viathe connecting part 17 so that the bending device 3 has moved downwardsin the direction of the arrow F3 in FIG. 3. The loading roller 6 hasthus lowered the marginal sheet portion 2, which is still freelyprojecting in FIG. 2, onto the load reaction surface 10. Not only is aload then applied perpendicular to the load reaction surface 10 but, atthe same time, a pull is exerted on the marginal sheet portion 2 towardsthe free sheet margin. This occurs because the sheet 1 arched up infront of the loading roller 6 and because, under certain circumstances,the loading roller 6 presses somewhat into the sheet 1.

In the operating position of FIG. 4, bending of the free marginal sheetportion 2 has been completed. By pressurizing the hydraulicpiston-and-cylinder arrangement 19, the loading piston 26 has now beenextended and comes into engagement with the abutment surface 25. Acorresponding pressure is accordingly exerted, via the pressing ram 5,on the surface of the marginal sheet portion to be bent until the sheet1 has cooled at this location and the desired hardening of the laminatedplastic sheet has taken place.

It is clear from FIG. 4 that the pressing roller 6 now has no functionand is free.

It can be seen from the illustration in FIG. 5 that bending anglesgreater than 90 degrees can be obtained with the arrangement accordingto the invention, i.e., an angle smaller than 90 degrees exists betweenthe underside of the sheet 1 and the marginal sheet portion 2 to bebent.

FIG. 6 shows a feature of the arrangement in accordance with theinvention, namely, the provision of inserts 21 and 22 which are disposedin the region of the curved reaction surface 4 and bear against theunderside of the sheet 1 in the area of the bend. It is seen thatdifferent inserts 21 and 22 can be stored depending upon the bendingangle and the bending radius so that a conversion of the machine fromone bending angle to another can be performed rapidly and withoutproblem.

I claim:
 1. An apparatus for forming a laminated sheet, comprising means for clamping the sheet during forming; means for supporting the sheet, said supporting means being provided with a bent surface for bending the sheet and an abutment surface which defines a predetermined bending angle; means for bending the sheet, said bending means including a carriage, a first member on said carriage for urging the sheet against said surfaces to thereby bend the sheet, a second member on said carriage for holding the sheet against said abutment surface following bending of the sheet, and means for urging said second member against said abutment surface, said urging means including a piston-and-cylinder unit; means for guiding the carriage, said guiding means including a track having a section which is substantially parallel to said abutment surface, and said section and said abutment surface being adjustable to vary the angle of bending; and an abutment fast with said track, said abutment being engageable by said piston-and-cylinder unit to thereby urge said second member against said abutment surface.
 2. The apparatus of claim 1, wherein said clamping means is provided with a pair of substantially flat clamping surfaces.
 3. The apparatus of claim 1, wherein said bent surface and said abutment surface are substantially in register with one another, said clamping means being provided with a clamping surface which is inclined to said abutment surface and is substantially in register with said bent surface and said abutment surface.
 4. The apparatus of claim 1, wherein said first member comprises a roller and said second member comprises a plate.
 5. The apparatus of claim 1, wherein said first and second members are constructed as a unit.
 6. The apparatus of claim 1, wherein said track has another section which is adjustable about an axis substantially paralleling said surfaces.
 7. The apparatus of claim 1, wherein said carriage is provided with rollers which engage said track; and further comprising means for displacing said carriage along said track.
 8. The apparatus of claim 1, wherein said piston-and-cylinder unit is hydraulic.
 9. The apparatus of claim 1, wherein said bent surface is defined by a removable insert having a predetermined radius.
 10. The apparatus of claim 9, further comprising additional inserts having radii different from said predetermined radius. 